Electro-optic systems have been developed to facilitate transmission of data, images, signaling, etc., via fiber optic links, where systems such as wavelength-division-multiplexing (WDM) and dense WDM (DWDM) have been developed to increase the channel capacity (e.g., bandwidth) of such electro-optic technologies. Generally speaking, channel routing and switching has been attempted to facilitate directing and access to data, etc., at a particular node, where an optical switch can be utilized to direct one of more wavelength streams. Early electro-optic switching utilized optical-electrical-optical (OEO) techniques to extract a light stream of a given wavelength, convert the light stream to an electrical signal to pass the data contained in the light stream through the electro-optic switch and subsequently reconvert the electrical signal back into a light stream to facilitate transmission of the data through a subsequent fiber optic link comprising the electro-optic system.
To improve the efficiency of electro-optic circuits, technologies have been developed to address the inefficiency inherent in OEO approaches (e.g., the conversion from light to electric form and back to light form), whereby newer technologies have attempted to guide a light stream without having to convert to an electrical signal.
Waveguide systems have been developed to facilitate routing a light stream from a single waveguide channel into two channels (e.g., a Y-splitter), or from two channels to another two channels (e.g., an X-splitter), and vice-versa. A switching unit can comprise two waveguides, which have a small branching angle at the point at which the two waveguides meet. Waveguides are formed in a layer of optically nonlinear polymer possessing an initial isotropic refraction index (RI)=nplate. By heating a localized region of the layer (e.g., a portion to form a desired waveguide path) to a temperature above the glass-transition temperature, partially orientating dipolar moieties (e.g., by ‘poling’ with an applied voltage) in the localized region, and subsequent slow cooling, an optically anisotropic region having RI=nwv is formed with the optical axis directed along an electrical field where nwv>nplate. The optically anisotropic region of the layer, having RI=nwv, forms a core waveguide with the remainder of the layer, having RI=nplate, being used as cladding media to encapsulate the waveguide and constrain a light stream(s) therewithin. With a Y-splitter or an X-splitter, an active zone can be formed at the junction of the respective waveguides. The active zone can comprise switching electrodes, which can be used to apply a modulating electric field to change the RI in the active zone, which changes the phase of a light beam from a first phase to a second phase to facilitate switching propagation of the light beam from a first branch to a second branch of the respective splitter.
Depending on the magnitude of the induced RI, the light stream entering into one of waveguides can continue propagation through the waveguide or be switched to another waveguide. A disadvantage of this approach is the heating and cooling operation required during the poling operation has to be closely controlled in terms of the temperature above the glass transition temperature and also the rate of heating to, and cooling from, the temperature, as well as ensuring the heating and cooling operation is confined to the waveguide region and does not extend into the adjacent regions which will subsequently form the cladding layer having an RI=nplate. Heating of the active zone can be performed by means such as a powerful microheater with a rapid rate of heating, however, the cooling operation can result in unwanted heat dissipation into the cladding region. Further, temperature control of the active region is required during operation of the switch as a shift in operating temperature can result in a shift in the RI of the active region being such that a light beam is directed to the incorrect waveguide.
Another conventional approach is an all-optical switch comprising a pair of waveguides which are within evanescent coupling distance of a microresonator, where the microresonator is in the form of a ring or disk-type (e.g., a whispering-gallery-mode (WGM) type) and heat is applied to the microresonator by means of a light source, such as a laser. In a first mode of operation (i.e., no applied heating) a light stream comprising a plurality of wavelengths propagating in a first waveguide undergoes no effect by the microresonator and continue to an exit of the first waveguide. However, in a second mode of operation where heating is applied to the microresonator, evanescent coupling can cause excitation in the first waveguide, where fluctuation in the microresonator disk can generate a fluctuation in the wavelength of the light stream from a first wavelength (e.g., the wavelength occurring when no heat is applied) to a second wavelength (note: that wavelengths other than the first or second wavelength comprising the light stream continue unaffected). Hence, a wavelength in a light stream can be extracted from a first waveguide (e.g., a throughput channel) and a corresponding light stream of a second wavelength can be generated in a second waveguide (e.g., a dropout channel).
As with the previously mentioned X or Y-splitter approach, however, localized heating and cooling of a polymeric material (e.g., comprising the microresonator) is applied to effect a change in RI in the active zone of the waveguide, where, with extended operation, the efficiency with which the heat activating the thermal shifting of the microresonator may be hindered owing to overall heating of the switch system which leads to incorrect operation of the switch, e.g., the desired wavelength light stream does not undergo a wavelength capture operation or a light stream of an incorrect wavelength may be generated. Further, the aforementioned systems are difficult and expensive to manufacture.
A further approach is a plate comprising parallel waveguides having a mutually perpendicular direction formed in an optically transparent region possessing electro-optical or/and acoustic-optical properties. The RI of the plate as a whole=ncladd, while portions of the plate used as core waveguides have an RI=ncore>ncladd. Increasing the RI of the core portions can be achieved by ion implantation/bombardment to form the waveguide core, while any portions of the plate not undergoing implantation act as cladding media. Electrodes can be placed at a waveguide junction to facilitate application of an electrical voltage to redirect a particular wavelength in the light stream, e.g., by adjusting the RI of the waveguide at the junction. By utilizing electrode(s) of a specific shape, e.g., a plurality of fingerlike extensions, a diffraction grating can be formed where a light stream of a particular wavelength can be extracted at a first finger electrode while a light stream of another wavelength can be extracted at a second finger electrode, producing a diffraction effect. By controlling the gap between adjacent fingers of an electrode(s) and further adjusting the electric voltage between the electrode fingers, different wavelength light (and corresponding color, if applicable) can be extracted from a light stream in a first waveguide and directed towards a second waveguide, at the end of which a device can be located, such as one or more pixels in a visual display system, a photosensitive element, etc. The electrodes can be in a curved form in a planar direction, and can hence act to bend the light stream through a given angle. While only a particular degree of bending can be obtained at an electrode, by forming electrodes with a plurality of bends, the light stream can be bent through a greater total angle than is achievable by a single electrode alone. The bent electrode approach is termed a total internal reflecting (TIR) optical energy redirector.
An example of a conventional waveguide system 100 is illustrated in FIG. 1A. A substrate 101 is formed from a transparent material having electro-optical properties, where the base material 101 has a RI=n1. Ion implantation/bombardment forms a plurality of waveguide regions 102, where the waveguide regions have a RI=n2, where n2>n1, with base material 101 acting as cladding material for waveguides 102. At regions 103, where the waveguides 102 cross, electrodes 104 can be placed to facilitate formation of switching regions at 103, where electrodes 104 can be placed on either side of a waveguide, with the waveguide sandwiched therebetween. To minimize light loss in the electrode region, a layer of dielectric material of ˜10 nm in thickness can be used as a cladding material. Where no voltage is applied by the electrodes, any light stream entering at 105 or 106 will be unaffected with regard to direction and will exit the respective waveguides at 107 or 108. Where voltage is applied by the electrodes, any light stream entering at 105 or 106 will be affected with regard to direction and will exit the waveguides at 109 or 110, respectively.
Turning to FIG. 1B, an example waveguide system 110 of the waveguide system 100 is illustrated comprising waveguides 102, with bent electrodes 111 placed to effect re-direction of a light stream entering waveguides 102 at input 105. Example waveguide system 110 comprises two TIR reflectors comprising electrodes 116 and 117 and domain regions 115 and 118. In a state of no voltage being applied to any of 115-118, a light beam entering waveguides 102 at input 105 will continue unaltered to exit at 107. However, the TIR reflector regions act to reflect the light stream to a greater degree than is achievable by the electrodes alone and hence a light stream can be directed to the other waveguide 102 and exit at 109. Such an approach is comparable to the aforementioned Y-splitter apparatus.
Another example waveguide system 120 of the waveguide system 100 is presented in FIG. 1C, where, in an unenergized state, a light stream can enter a waveguide 102 at either 105 and pass unaltered through to 107 or enter at 106 and pass through to 109. However with a voltage applied at electrodes 112, a light stream entering at 105 is redirected to output 109, or a light stream entering at 106 is redirected to output 107. The redirection of the light stream is effected by polarization of domain 138, whereby the polarization effect results in formation of a polarized wall, having a different RI to that of the unpolarized state, which acts to reflect the light stream through 90°. Such an approach is comparable to the aforementioned X-splitter apparatus.
Example systems 110 and 120 use a domain that changes RI and polarization in the presence of an electric field, and thereby issues relating to thermal effects are negated. However, systems 110 and 120 incur the high costs of a monocrystal layer having a very high uniformity of structure, the difficult capability to achieve small device size, the technological complexity required for formation of switching elements, and further, the difficulty of incorporating a small-sized switch with a set of standard input and output waveguides for which switching it is intended.